Short-range and high-resolution ultrasound imaging using an 8 MHz aluminum nitride PMUT array

Ultrasound imaging uses costly bulk piezoelectric transducers and high voltage (200V+) electronics. Low-cost and low-voltage ultrasound transducers would enable many new applications in healthcare, biometrics, and personal health-monitoring. Here, we demonstrated short-range (~mm) and high-resolution (<;100 μm) imaging based on piezoelectric micromachined ultrasonic transducers (PMUTs) and a 1.8 V interface ASIC. The PMUTs use piezoelectric Aluminum Nitride (AlN), which has the advantages of low-temperature (<;400 °C) deposition and compatibility with CMOS fabrication but has a relatively low piezoelectric constant (e₃₁=-0.5 C/m²), making detection of ultrasound signals from tiny (50 μm) PMUTs a challenging task. To solve this problem, we developed an ASIC with a low-noise analog front-end pre-amplifier that is impedance matched to the PMUT. Furthermore, a novel beam-forming and scanning method was demonstrated to achieve a sub-100μm focus size and 70 μm scanning step. Pressure map measurement from phased PMUT array and pulse echo imaging results were demonstrated using 1-D and 2-D phantoms.